Generally, electrical resistance heaters, fuel gases or the like are heat sources for heating iron cooking plates to cook steaks, grilled meat, okonomiyaki (meat and vegetable pancakes), pancakes, hot dogs, hamburgers or the like. However, the gas burning method causes gas and heat problems, particularly the danger of a possible gas explosion. Therefore, the gas burning method is not a preferred heating method for restaurants. Another problem caused by the gas burning method is low energy conversion efficiency (thermal efficiency); the conversion from gas to heat is only about 20-30% efficient. An additional problem is difficulty in controlling the temperature in the gas burning method. Temperature control is also difficult in electrical resistance heaters.
In order to solve the above-noted problems, an electromagnetic induction heater comprising six induction coils, positioned vertically and in a circular configuration and connected in a delta connection supplied with a low-frequency electric power source of 50 Hz or 60 Hz, has been disclosed in U.S. Pat. Nos. 4,999,467, 5,053,593, and European Patent No. 0,380,030A1.
However, the inventions disclosed in U.S. Pat. Nos. 4,999,467, 5,053,593, and European Patent No. 0,380,030A1 present the problem that only the central part of an iron cooking plate is heated directly by the coils and that the peripheral part of the iron cooking plate can be heated only by heat conduction. As a result, the electromagnetic induction heater of the above patents cannot heat a wide area uniformly.